The present disclosure relates to a method for producing a coated pull-out guide, for example, for baking ovens. The pull-out guide includes a rail on which at least one further rail is displaceably supported by rolling elements. The rolling elements are guided along tracks on the rails.
EP 1 607 685 discloses a coating method for a telescopic rail in which a PTFE coating is applied to chrome-plated structural steel or stainless steel. For pre-treatment of the telescopic rail, first a cleaning process is carried out by means of temperature treatment and then a surface treatment for roughening the surface by sand blasting. However, this type of pre-treatment is labor-intensive and there is the risk that residues of the blasting material will remain on the running surfaces of the telescopic rail. That would disadvantageously influence the running property of a pull-out guide produced using the rail. In addition, a high expenditure of energy must be applied during the thermal surface treatment. The individual parts of a pull-out guide are treated and the telescopic rails are only mounted after applying the method described.
The present disclosure thus relates to a method for producing a coated rail which is configured to be efficient with respect to process technology, cost-optimised and energy-efficient.
The present disclosure therefore relates to a method for producing a coated pull-out guide as further disclosed and described herein, including the appended claims.
In the method according to the present disclosure, a coated pull-out guide is produced which includes a rail on which at least one further rail is displaceably supported by rolling elements. The rolling elements are guided along tracks on the rails. The pull-out guide, with the rails and the rolling elements, is initially assembled into a unit. A metal surface of at least one rail of the pull-out guide is then cleaned by a mechanical and/or chemical cleaning method before applying a coating to the cleaned metal surface.
As a result of the mechanical and/or chemical cleaning, it is within the scope of the present disclosure to avoid an additional thermal treatment which involves a high energy consumption and longer dwell time in a heat chamber. During the chemical and/or the mechanical cleaning process, according to the present disclosure, the adhesive forces of impurities on the metal surface are reduced in such a manner that the impurities can be removed by wiping or are carried away by the cleaning agent. When using a mechanical cleaning process according to the present disclosure, an additional optional step to roughen the metal surface can be omitted. This is because the surface cleaning and roughening can be carried out simultaneously in one step in the cleaning process. In this case, according to the present disclosure, a combination of chemical and mechanical cleaning can also be carried out, for example, by additionally setting a liquid cleaning agent in vibration by an ultrasound transducer. Due to the subsequent treatment of the metal surface, a reduction in the adhesion of dirt, an increase in protection against scaling, an increase in corrosion protection and/or an increased scratch resistance are achieved.
The cleaning of the metal surface, may, according to the present disclosure, take place at a temperature of 0 to 200° C., or, for example, at ambient temperature. As a result, any heating of the pull-out guide during cleaning is reduced to a minimum.
In one embodiment according to the present disclosure, the tracks on the rails remain coating-free when applying the coating so that a high running quality is achieved. The coating-free tracks can be formed, for example, by masking or covering the tracks or by pushing the rails together during the coating process. The pull-out guides, may, according to the present disclosure, be located during the coating process in the mounted, inserted state. For example, the tracks and rolling elements cannot be contaminated by coating material during coating by the spray method.
When the chemical cleaning process of the metal surface, according to the present disclosure, is used, the process may comprise the following steps:                i) inserting the pull-out guide into a cleaning chamber,        ii) cleaning the pull-out guide from impurities by wetting the surface with a cleaning solution,        iii) transferring the contaminated cleaning solution into a processing unit,        iv) processing the cleaning solution by removing impurities from the cleaning solution,        v) transferring the processed cleaning solution into a storage tank, and        vi) returning the cleaning solution into a cleaning chamber.        
By circulating the cleaning agent during the cleaning process, waste products of the cleaning agent can be largely avoided. The process control additionally enables fully automatic cleaning before the coating step.
The cleaning of the metal surface can be accomplished by a blasting, or mechanical process. For example, ice blasting, ice blasting with blasting media additives, carbon dioxide pellet blasting and/or carbon dioxide snow jets can be used. These blasting process methods are advantageous since they remove both impurities and also act abrasively so that cleaning and surface roughening take place in one step. At the same time, no blasting agent residues are left on the tracks and other regions of the rails. As a result of using a blasting media additive when ice blasting, a rinsing step may be necessary to release and/or wash away the blasting medium additive. Salts, having a low water solubility, are advantageously added to the ice jet as a blasting additive. The salts increase the abrasiveness and can be removed by a rinsing step if required.
The cleaning of the metal surface can preferably be accomplished by an ultrasound process. In this case, a solvent can be applied to the surface which releases impurities from this surface by ultrasound wave initiated cavitation. Additionally or alternatively, instead of the solvent, cleaning additives or solvent mixtures can be used which reinforce the cleaning action of the solvent. These can, for example, be other solvents of different polarity, tensides, acids or alkalis and salts.
The cleaning of the metal surface, according to the present disclosure, can furthermore be accomplished by a plasma process. In this case, plasma is produced by ionization of oxygen at room temperature under vacuum, or low-pressure plasma, ambient pressure, or atmospheric plasma, or excess pressure, or high-pressure plasma. The reactive oxygen ions burn organic impurities cold to form carbon dioxide without additional thermal loading of the pull-out guide. The process is, therefore, very environmentally friendly since only oxygen is used for cleaning and non-toxic carbon dioxide, CO2, and water, H2O, are predominantly produced as reaction products. In addition, the vacuum technology of the plasma cleaning process can be used for a subsequent plasma coating process of the pull-out guide which allows the expenditure on apparatus to be reduced.
According to another embodiment of the present disclosure, the cleaning of the metal surface is accomplished by a laser cleaning which can eliminate severe contaminants particularly precisely.
Alternatively or additionally, according to the present disclosure, a chemical cleaning of the metal surface can take place. Liquid carbon dioxide, alkaline solutions, and/or mordants can be used for this purpose. An electrolytic cleaning using alkaline and/or acidic solution can furthermore be accomplished. When using carbon dioxide it is an advantage that this is safe and is easy to separate from the dissolved impurities. Alkaline and acidic solutions are readily available so that they are inexpensive to use. Processing of these solutions is also readily possible. Cleaning solutions used for cold cleaning and spray degreasing contain a different fraction of non-polar solvents depending on the type of impurities. These cleaning solutions can be processed by distillation and then returned into the cycle, for example, an etching process can also lead to a specific roughening of the surface. The cleaning and a possible roughening of the surface can thus take place in one process step, according to the present disclosure.
It is advantageous, according to the present disclosure, that the coating comprises PTFE, PEEK, PEK and/or inorganic-organic hybrid polymer-containing materials. These coatings have proved particularly favorable for food technology areas of application. At the same time, in particular, coatings containing inorganic-organic hybrid polymer-containing materials can also withstand temperatures above 300° C. which are attained by a conventional domestic oven in pyrolysis mode.
At the same time, it is advantageous, according to the present disclosure, if the application of the coating is accomplished by a plasma coating process since the plasma coating process has a better material adhesion with the metal surface of the pull-out guide. The spray process is advantageous, according to the present disclosure, since only the outer surfaces of the mounted pull-out guide are coated. The tracks, the rolling elements and rolling element cages remain coating-free, unlike in the conventional dipping process. The running properties of the pull-out guide are not negatively influenced. An improvement in the material adhesion is also advantageously ensured, according to the present disclosure, by applying a functional coating by a sol-gel process. A coating according to the sol-gel process can also be applied, according to the present disclosure, by the spray process.
Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings.